Tube Substitution Guide book

I'm new to tube equipment and recently completed a ST-120 amplifier with about 20 hours on it.It has been a very rewarding experience and great source of achievement for me not to mention it sounds unbelievable. I inherited from my father a couple of tube testers and found a small book inside one of them titled "1966 tube caddy" Tube Substitution Guidebook.I'm trying to educate my self on tube rolling and found it interesting that this book lists direct substitutions only and ranks them by E=Excellent or G-Good and has sections listed for Receiving, Commercial & Industrial, American-Foreign tubes.I have seen the recent posts and understand this is a subjective topic and should let my ears guide me as to what sounds good however after looking at many reputable dealers, private parties and on e bay I could invest a substantial amount of money without hitting audio bliss so would this be a good starting guide?I have the kit supplied 5814 installed and while the amp sounds great it does sound a little bright to me, the sub book lists them as excellent so do I need to be patient until I have 100 hours or more to see if they smooth out?If anyone is interested in the info from the book I would be happy to photo and post sections for them as time allows.Thanks

I recently retubed my ST35 with a full set of RAM Labs selected tubes and it has never sounded better. What finally convinced me to go that route was something I read on the RAM website:

Here's an analogy for the mechanically-minded.

Imagine a VW-type engine where the cylinders are opposed and made separately, and the manufacturer puts together engines where the pistons, rods, and cylinders are not very uniform. In this engine there is only one arm on the crank (like the driver in our amplifier), and all the rods are connected to it so that they all have the same length of throw. One "pair" of pistons should top out together when the other pair hits bottom. If any of them has a short rod, it will achieve less compression and therefore less power.

If he matched the rods and selected cylinders of the same bore, he would then get equal power per constraint of that one crank. With unequal push rods, we're going to end up with very different compressions at the end of the stroke, and thus very different output power from each cylinder.

I replaced new issue Genalex EL84s which had gone bad on me after less than a year with a properly matched set of Russian EL84s. The depth and clarity I'm getting is mind-boggling! Up until this point I hadn't had a very good opinion of Sovtek. But that analogy I quoted makes sense to me. Tube circuits allow for some variation, but if you want the most accurate performance then a properly matched set is imperative.

Just a warning: I have the 1977 copy of this book. Had it since it was new. The book lists possible substitutes based on the tubes pinout. There is no accounting for power dissipation, or any other parameters. The book just says to select the substitute from the area of the chart that the needed type falls in. They are broken down in sub groups. You will still find things like 6l6 and all its variants interchangeable with the likes of 6V6, 6K6, 6F6, and others. Sometimes there are mistakes too, though, just picking up the tube and the possible sub and putting them together would make my point clear. Of course it helps to have both tubes to see if there are major physical differences. I once subbed a 6GH8A for a 6U8A in a communications receiver and then would have had to perform major adjustments to get the set back in alignment. I left well enough alone. With audio tubes, the circuits may be less critical, but I still would rather replace with a correct type.

anbitet66 wrote:Just a warning: I once subbed a 6GH8A for a 6U8A in a communications receiver and then would have had to perform major adjustments to get the set back in alignment. I left well enough alone. With audio tubes, the circuits may be less critical, but I still would rather replace with a correct type.

corndog71 wrote:I replaced new issue Genalex EL84s which had gone bad on me after less than a year with a properly matched set of Russian EL84s.

An aside - the N709/EL84 Genalex will not survive if asked to operate beyond dissipation specs. If the tubes were passing over about 35 ma. of cathode current then they were above spec (12 watts). With today's higher AC line voltage that is VERY likely unless the amp has been modified to reduce the current.

corndog71 wrote:I replaced new issue Genalex EL84s which had gone bad on me after less than a year with a properly matched set of Russian EL84s.

An aside - the N709/EL84 Genalex will not survive if asked to operate beyond dissipation specs. If the tubes were passing over about 35 ma. of cathode current then they were above spec (12 watts). With today's higher AC line voltage that is VERY likely unless the amp has been modified to reduce the current.

corndog71 wrote:I replaced new issue Genalex EL84s which had gone bad on me after less than a year with a properly matched set of Russian EL84s.

An aside - the N709/EL84 Genalex will not survive if asked to operate beyond dissipation specs. If the tubes were passing over about 35 ma. of cathode current then they were above spec (12 watts). With today's higher AC line voltage that is VERY likely unless the amp has been modified to reduce the current.

The short life was the result.

I run mine at 27mA.

If you measure from plate to cathode and the voltage measures 450 or higher even 27 ma. puts the dissipation at 12.15 watts (12 is the max).

Do you leave the amp on all the time - could you estimate how many hours of use it had on the Genalex tubes? Thanks!

corndog71 wrote:I replaced new issue Genalex EL84s which had gone bad on me after less than a year with a properly matched set of Russian EL84s.

An aside - the N709/EL84 Genalex will not survive if asked to operate beyond dissipation specs. If the tubes were passing over about 35 ma. of cathode current then they were above spec (12 watts). With today's higher AC line voltage that is VERY likely unless the amp has been modified to reduce the current.

The short life was the result.

I run mine at 27mA.

If you measure from plate to cathode and the voltage measures 450 or higher even 27 ma. puts the dissipation at 12.15 watts (12 is the max).

Do you leave the amp on all the time - could you estimate how many hours of use it had on the Genalex tubes? Thanks!

No, I only listen a couple of hours at a time. If I'm lucky I get to listen a few times a week at the most. I should probably also mention I'm not using the classic cathode resistor bias circuit. I'm using Dave Gillespie's EFB which works better with regards to AC line changes. I'm not convinced the Genalex tubes were properly matched. If I had to guess I would say I had about 700 hours on them give or take. I'll try measuring the plate to cathode but I'm pretty sure the circuit is solid.